1 March 2011

3 minute read

North America

Putting cows out onto pasture in the spring needs to be timed correctly to ensure that pasture land stays healthy and productive. Pastures should not be grazed until after the three-leaf stage. This is when taller growing pasture plants are at least six-to-eight inches tall and lower growing ones are four-to-six inches tall.

“If you have a high proportion of legumes in the pasture, do not graze until the plants are 8-to-12 inches tall,” says Grant Lastiwka , Ag-Info Centre, Alberta Agriculture and Rural Development.

“Grazing native range before the third leaf stage can result in the loss of over 60 per cent of the potential forage yield. Grazing a pasture too early will result in the vegetation being removed before the plants have had a chance to replenish their root reserves. Grazing one week too early in the spring will sacrifice three weeks of grazing in the fall.”

Rotational grazing is one of the management practices that can improve pasture health. As a general rule, forage plants need at least one month of rest to regrow properly and to replenish their nutrient levels. Overgrazing can be very detrimental to pasture land. It is important to leave some plant material behind so the plants will continue to grow. With tall growing grasses leave a minimum of four to eight inches of plant residue; with low growing leave four-to-six inches of plant residual; the more leaf area remaining, the more photosynthetic material available to replenish root nutrient reserves.

“Cattle should be moved based on the growth rate of the pasture and the height of the forage,” says Grant Lastiwka. “Forages grow more rapidly in the spring, so cattle will need to be rotated more often (three days or less), and close attention should be paid to make sure the cattle are leaving more residual behind in spring grazing moves. The residual left in the spring grazing incident determines the plant speed of recovery and yield (or lack of yield) later in the grazing season. As grass growth rate declines through the summer, the frequency of rotation must be decreased to balance pasture use and recovery periods. To accomplish slower moves and longer grazing periods, less residual is left than was in the spring grazing period.”

Over-grazing is a function of timing and duration of grazing. Over-grazing occurs when the plant is grazed before it has had time to recover from overwintering or during the growing season, from the previous grazing. Pasture plants need time to produce above ground growth before they can put reserves down into the root system.

Root health is very important for the plant’s ability to grow throughout the growing season. Most grass root systems will stop growth within 24 hours of severe defoliation and in most cases they will not resume growth for several days after. The more rest given in the active growing season to an over-used pasture the better. That is why spring, the period with the most rapid plant growth capability is the most effective time to start using wise grazing management.

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